1. Field of the Invention
This invention relates to a carbon dioxide absorber and its manufacturing method using sludge which is discharged typically as a result of manufacturing fresh mixed concrete or concrete secondary products, and also relates to a method for absorbing carbon dioxide contained in exhaust gas by using sludge.
2. Description of the Prior Art
The cement- or concrete-related industries discharge exhaust water including sludge, as result of manufacturing fresh mixed concrete or concrete secondary products, or washing concrete mixers, hoppers, agitator trucks or wet dust collectors. Such sludge-containing exhaust water includes 60 percent of cement particles of a mean grain size of 10 .mu.m or less and their hydrate, such as particles of calcium hydroxide (Ca(OH).sub.2), and exhibits a strong alkali.
Heretofore, sludge-containing exhaust water has been treated by separating it into solid components and water by using a precipitator, a filter press or other appropriate equipment, so as to dispose the solid components as a waste and to reuse or release the water after pH adjustment using sulfuric acid (H.sub.2 SO.sub.4), hydrochloric acid (HCl), carbon dioxide (CO.sub.2), or the like.
A conventional system for treatment of such exhaust water is outlined below with reference to FIG. 3 which has been taken from "Simple Knowledge on Cement and Concrete" (by Junji Yamada et al., Kajima Shuppankai, Feb. 10, 1983, p. 256). FIG. 3 shows a treatment process of such exhaust water. Sludge-containing water discharged after cleaning of a plant such as mixers, hoppers, etc. (1) and that discharged after cleaning agitator trucks (2) are treated by a solid separating process. Solid components, such as ballast and sand, separated from the sludge-containing water are held as reusable materials, and the remainder water is sent to a subsequent treatment step, that is, a precipitating/separating step (6). Also, exhaust water from wet dust collectors (4) and that used for watering factory facilities and aggregates (5) are collected, and sent to the precipitating/separating step (6). Supernatant water, obtained in the precipitating/separating step (6) and not containing sludge and other solid components, is pH-adjusted in a neutralizing step (7), and released thereafter. Another part of the exhaust water obtained in the precipitating/separating step (6) and including solid components and a certain amount of water is adjusted in concentration to be reused for making concrete. The other part of the exhaust water obtained in the precipitating/separating step (6) and consisting of sludge is dewatered to be disposed as a final waste.
Existing treatment systems, as referred to above, certainly envisage the reuse of recovered sludge-containing, concentration-adjusted water for manufacturing concrete; however, they have no significant consideration on effective use of sludge itself.
In addition, existing treatment systems have no significant countermeasure on carbon dioxide contained in exhaust gas produced in cement manufacturing plants, thermal power plants and iron mills which produce a large amount of heat and gas.